Method of forming web material



Oct. 2, 1945. MELTQN METHOD OF FORMING WEB MATERIAL Filed April 18, 19422 Sheets-Sheet l Oct 2, 1945. R. MELTON 2,385,873

METHOD OF FORMING WEB MATERIAL Filed April 18, 1942 2 Sheets-Sheet 2fiveniaz' POM/5 L. MfL TON Lfarne Patented Oct. 2, 1945 METHOD OFFORMING WEB MATERIAL Romie L. Melton, Niagara Falls, N. Y., assignor toThe Carborundum Company, N. Y., a corporation of Delaware Niagara Falls,

Application April 18, 1942, Serial No. 439,585

6 Claims.

This invention relates to an improved method of manufacturing flexiblefibrous webs of nonlamellar felted structure from a plurality of thincarded unwoven membranes, and also relates to apparatus for carrying outsaid process. More particularly, it is concerned with a method ofelectrically weaving and interlocking the individual fibres of each ofseveral membranes constituting the web with the fibres of the othermembranes by exposing or subjecting the membranes to the influence ofelectrostatic fields of sufficient strength to electrically charge thefibres and upend them in a manner suitable for intermingling themembranes one with the other to form a nonlaminated structure, but ofinsufiicient strength to rupture or harmfully disturb the membraneitself. The invention further relates to the formation of flexible websin the above manner in which various modifying agents are incorporatedin the web to impart specific desired properties to all or portions ofthe web structure.

The general process heretofore used for making felted fibrous Webs froma plurality of thin carded fibrous membranes is best illustrated in thePatent No. 2,055,411 to Edward Hurst. There the weaving and interlockingof the fibres has been attained by the use of currents of air or othergas which are passed through the membranes to disturb the normallyhorizontal arrangement of the fibres and is referred to therein as an"aerodynamic weaving action. However, the control of air currents,regardless of how gentle, is at best difiicult and subject to surges andfluctuations which interfere with a uniform interweaving action, and attimes even cause rupture or non-uniform distribution of the membrane,holding up operation until the condition is corrected or the breakrepaired. The use of an aerodynamic weaving process also requires achamber or other substantially enclosed space for passage of themembranes so that an atmospheric or gaseous pressure differential can bemaintained from one side of the membrane to the other side and therebycreate and promote the necessary weaving action.

An object of the present invention is to provide an improved method andapparatus for weaving and intermingling the individual fibres of uchwebs by electrostatic means, which process is capable of closer controland otherwise overcomes or obviates the undesirable features of thepreviously employed aerodynamic methods as will readily become apparentas the description of the present process and apparatus proceeds.

In accordance with the present invention as each thin fibrous membraneis removed from a carding machine it is deposited upon a moving endlesssupport or carrier and passed through an electrostatic field whereuponthe individual fibres of the membrane are given an electrical chargewhich causes the ends of the fibres to be upended from the horizontalplane of the membrane. While the fibres of the membrane are in such anelectrified condition suitable for interlocking, additional fibrousmembranes are similarly electrified to upend their respective fibres andin that condition superimposed upon the initially deposited and stillelectrified membrane whereby the fibres of each membrane, due to theirelectrical charges, are'woven and interlocked with the fibres ofadjoining membranes. As a further means to promote a weaving action, andparticularly a lateral or patterned weaving, certain of the electrodeswhich serve to create the electrostatic fields may be positioned orreciprocated laterally so as to give a sidewise orientation or pull .tocertain of the fibres. Also, the lower electrode of an electrode pairmay be formed with a multiplicity of points or of an open grid shape soas to impart a controlled but variable orienting and weaving action tothe fibres, and by reason of the pointed projections produce a number ofsmall intense electrical fields which give added penetrating power andvertical weaving together of the fibres of the various membranes.

Moreover, modifying agents such as waterproofing compounds,anti-friction agents, fiexibilizers, adhesives and other fillers may beincorporated in the web at the time of making in order to render the webresistant to water or impart other specific desirable properties to allor certain controlled portions of the web.

This invention may be more clearly understood by reference to theaccompanying drawings, in which:

Figure 1 is a vertical diagrammatic cross-section of an apparatus formaking flexible fibrous webs in accordance with the teachings of thepresent invention;

Figure 2 is an enlarged vertical cross-section of that portion of theapparatus used for the electrostatic weaving of the fibres and showingone of the electrode pairs in further detail;

Figure 3 is a vetrical cross-section of a modi fied form of theapparatus shown in Figure 2; and

Figure 4 is a perspective view on an exaggerated scale showing a p rtionof a fibrous web formed by my method and before the web is im pregnated.

Referring further to the apparatus shown in Figure 1, the apparatuscomprises a plurality of carder assemblies suitably spaced apart andconsisting of carding rolls 2, stripper rolls 3 and combs 4 for removingthe fibrous carded membranes 5, 6, 1 and 8 from the rolls 3. The cardedmembrane may consist of any animal, vege- .table or synthetic fibrousmaterial capable of being carded into yarn or sheet form. While cottonfibres have proven to be highly satisfactory for the {present rocess,other fibres suggested for use are'such natural fibres as wool, Jute,flax and the like, or any ofthe newer synthetic fibres such as glasswool, resinous or synthetic rubber fibres. Also, instead of having allof the fibres of the same material, one or more of the fibrous membranesmay be of a difierent fibre than the rest. Although only four carderassemblie are shown in Figure 1, any number of carders may be useddepending upon the desired thickness and type of fibrous web.

The carded membranes are fed by gravity onto a moving carrier belt 9which is slightly wider than the width of the deposited membranes andmay have upturned or flanged edges for guiding the oncoming membranesonto the moving support. The supporting conveyor belt may be anysuitable flexible, electrically non-conducting material, a rubberizedfabric belt sold under the trade name Ton-Tex" being found highlysuitable for the purpose. The conveyor belt is supported by the rolls land Ill, which are driven by suitable means (not shown), and the speedof the belt synchronized with that of the carded membranes in order thatno appreciable strain or pull is exerted on the thin membranes duringtheir deposition.

The initial membrane is deposited directly onto the conveyor belt andthen as each successive membrane 6, l and t is being deposited it ispassed through a series of electrostatic fields created betweenelectrodes l3, it and i5, which extend the full width of the conveyor 9and are positioned above and below the moving belt. As the membranesmove into the electrostatic field the individual fibres becomedisarranged and are shifted from their normal parallel position (assumedas a result of the carding operation) so as to assume upright or upendedpositions. While the loose ends of the individual fibres are in suchupstanding position, the membranes are brought together and theindividual fibres caused to intertwine and produce a firm homogeneousinterlocking structure which will be non-lamellar in final appearance,

An auxiliary or secondary electrode l5 having the same polarity as theelectrode i3 is positioned so that the gravity-fed membrane between itand the electrode i3 is approximately equidistant from the two upperelectrodes so that the fibres of the membrane are equally repelled from(or drawn to) the two and therefore maintained in equilibrium and guidedwithout disturbance to the carrier belt 9.

The source of electromotive force for creating the electrostatic fields,the effective potential of which is 20,000 volts or more, is notspecifically shown in the drawings, but is indicated by the positive andnegative symbols and connected to the electrodes I3, l5 and H! by theconnecting lead wires [6 and I1 respectively. The source ofelectromotive force may produce a continuous unidirectional current, anintermittent unidirectional current, or an alternating current dependingupon the particular requirements. The efiects of direct curent andalternating current electrostatic fields will be described hereinafterin greater detail. When a unidirectional current source is utilized itis preferable that the upper electrodes [3, I5 be connected to thenegative terminal and the lower electrode H be connected to the positiveterminal. However, if desired, the polarity of the electrodes may bereversed, and as a safety measure it is desirab e aaeaers that the loweror bare metal electrode be grounded.

Fibres leaving the carder assembly are arranged in a generally parallelposition which is normally produced by the carding action. If depositedon the carrier belt in this state the fibres assume for the most part aposition substantially parallel to the surface of the belt. With theapplication of additional fibrous membranes, the several layers would bemerely stacked one on the other and a laminated web produced whichseparates readily. Instead, it is desirable that an interlocking fibrousstructure be produced in which most of the fibres of each membraneproject upwardly at acute or right angles to the surface of the web andnot only intertwine with one another but also interlock and knittogether with the fibres of the succeeding superimposed layers. Thisaction is accomplished in an improved manner by the present processemploying an electrostatic intermingling action.

The electrostatic means for accomplishing this action is shown ingreater detail in Figure 2 or the drawings. The electrically chargedelectrodes and the particular manner in which they are positioned andused for reception of the fibrous membrane 6 and its juncture with thepreviously deposited membrane 5 is clearly depicted. The membrane 8 isfed by gravity down and between the upper electrode 98 and the auxiliaryelectrode l5, both of which are similarly charged with a negativepolarity. Electrode i5 cooperates with electrode l3 in imparting anelectrostatic charge onto the fibres of the membrane 6 as it is fedtherebetween and onto the previously deposited membrane 5. It alsoserves in conjunction with the rear portion of lower electrode M toelectrostatically charge and maintain the electrified condition impartedto the previously deposited membrane 5 so that the individual fibres 5aremain substantially upright and ready for interlocking with theupstanding fibres 6a of membrane 6. Thus the electrostatic field set upbetween the electrodes l3, Hi, It by application of a high electromotiveforce thereto serves to orient the outermost fibres of both membranes toan upended position highly suitable for interlocking and meshingtogether into a well-knit, non-laminated structure having a creditablyhigh strength.

The character and construction of the upper electrodes l3 and i5 are ofgreat importance in the operation of the apparatus and, preferably, areshielded by some poorly conducting material. The materials so usedshould be low enough in conductance that not enough current can flowalong or through it to cause arcing between the upper and lowerelectrodes, yet it should be sufliciently conductive to allow a smallleakage current to supply electrical charges to the membrane fibres inorder that they may be oriented and raised to an upright positionsuitable for interlocking with one another. Therefore the upper or highpotential electrodes l3 and i5 are formed of a poorly conductingmaterial 18 which completely surrounds the metallic plate l9 ofelectrode l3 and the metallic rod 20 of electrode l5. In speaking of apoorly conducting material this expression is used to distinguishbetween such materials as metals, carbon, or the like, which arerelatively good conductors of electricity, on the one hand, and highlyinsulating materials such assume current which flows through them isinsumcient to electrically charge the fibrous membrane, on the otherhand. For this purpose I have found molded materials, such as those soldunder the trade names of Micarta" and Bakelite" to be most satisfactory.However, other materials such as dry, knot-free wood can also be used.While these materials are so poorly conducting that they will not carryenough current to permit spark 'over or arcing between the upper andlower electrodes, they are sufiiciently conductive at the voltagesemployed to allow enough leakage current to pass and supply the smallamount of electrostatic charges required.

Ordinarily the lower electrode I4 is at ground potential and thus doesnot need to be encased by a poorly conducting sheath.

Figure 3 illustrates a modified form oi electrostatic apparatus forintermingling. and weaving the individual fibres oi successivelydeposited fibrous membranes to form a unified web structure, Thisapparatus differs from that shown in Figures 1 and 2 in that an uppercarrier belt is provided as well as two separate and distinctelectrostatic fields so that the fibrous material may be subjected tothe efiects of both a unidirectional electrostatic field and a pulsatingor alternating current field. In this particular apparatus the cardedmembrane 6 is fed by gravity onto a previously deposited membranecarried by the conveyor belt 3 and the superposed membranes moved into aunidirectional electrostatic field established between the electrodemembers 22 and 23. This unidirectional electrostatic field is producedby a source of electromotive force, the effective potential of which is20,000 volts, or more, not specifically shown in the drawings, butindicated by the reference characters SI and S2. Ordinarily the upperelectrode 22 is connected to the negative terminal Si of the source ofhigh voltage by the connecting wire 24 and the lower electrode 23 isconnected to the positive terminal S2 of the connector 25. However, thepolarity of the electrodes may be reversed when so desired. A body ofpoorly conducting material 26 is interposed between the high tensionelectrodes 22 and 23 so as to prevent electrical flash-over or arcingtherebetween.

As the membrane 5 and superposed membrane 8 move into the unidirectionalelectrostatic field the individual fibres of each membrane becomeelectrically charged and caused to become oriented or upended from theirnormal positions. There is also a translational i'orce produced by theaction of the electrostatic field on the charged fibres which causesthese individual fibres to tend to move toward the electrode of oppositepolarity and distend the thickness of the superposed membranes. Thus theair gap between the electrodes may in some cases be practically filledby the fibres of the extended membranes. Also, the upended ends of thefibres of both membranes intertwine and interlock to such an extent thatmembganes 5 and 6 become unified and indistinguisha le.

A carrier belt 21, mounted on supporting, rolls 28, 29, is drivensynchronously with the conveyor belt 9, by suitable means (not shown)and assists in moving the distended membranes through the unidirectionalelectrostatic field and into the ad joining alternating current fieldwhere the distended fibrous web is caused to collapse. This adjoiningfield of alternating polarity is established between the electrodemembers 3|, 32, by a source of high voltage alternating current, the

effective potential of which is 20,000 volts, or more, not specificallyshown in the drawings but indicated by the reference symbols S3 and 84.This source of alternating or pulsating current is connected to theelectrode members 3!, 32, by means 01 electrical cables 33 and 34,respectively. Channel members 35'and 38, of poorly conducting material,shield the electrode members 3| and 32 and prevent sparking orelectrical flash-over therebetween.

As the fibrous membranes pass from the unidirectional electrostaticfield into the closely ad- Joining field of alternating polarity, thedistended fibrous structure is agitated by the action of the alternatingelectrostatic field and the individual fibres caused to become morefirmly entwined one with another and interwoven or felted. The entireweb, as well as the individual fibres, is agitated by the action of thealternating field to such a degree that a partial consolidation of thedistended fibrous structure occurs as the material passes through thiselectrical field. Upon leaving the zone of electrical treatment theseveral membranes, which make up the web structure 31, are found to befelted together forming a unified web structure which does notdelaminate readily.

The apparatus illustrated in Figure 3 may replace each of theelectrostatic units shown in Figure 1 or, if desired, one such unit maybe located at the delivery end of the conveyor belt 9 and the severalfibrous membranes 5, 6, land 3 electrically felted in one singleoperation,

After the fibrous web has been built up to the required thickness andelectrically treated in the manner described it is ready to beconsolidated to a greater density for added strength. At the same timeit is desirable to incorporate a liquid adhesive binder within said webto bond the compacted fibres and produce a web of greater density havinga strength comparable to that of cloth.

The electrically woven fibrous web 38 moves from the terminus oftheconveyor 9 and passes between synchronously driven rolls 40, 4!, whereit is initially compacted. Passing from these compacting rolls the webis fed onto a moving conveyor belt 42, which is supported by thesynchronously driven rolls 43, 44, and delivered to the adhesive binderapplying rolls 45, 46. The liquid adhesive binder is contained in a pan41, which may be water-jacketed and heated as required. Lower roll 46 ispartially immersed in the liquid adhesive 49 and as it revolves aquantity of adhesive binder, determined by the adjustably spaced scraperbar 48, is applied into the web. Upper roll is adjustably spaced withrespect to the adhesive roll 46 and applies sufficient pressure tofinally compact the loose fibrous web as well as aid in forcing thebinder to permeate into and throughout the-web structure. The surfacesof both rolls 45 and 46 should be covered with a resilient layer ofabsorbing material.

The adhesive binder used to permeate and assist in maintaining theconsolidated condition of the web is preferably one of a flexible orresilient nature, such as latex, fiexibilized animal or vegetable glue,plasticized vinyl resin, plasticized urea formaldehyde resin, and thelike. Such flexible adhesives permit the retention or the naturalpliable character oi? the interlocked fibrous structure.

After the web is compacted and the proper amount of adhesive binderapplied therethrough. it is passed over a suction drum 50 and idler roll5| to asuitable chamber where it is dried or cured. This chambercontains an endless conveyor 52 which serves to festoon the web ontosupporting sticks 53 and to transport these sticks and looped materialto the moving rack 54. The speed of the moving rack M is so adjustedthat the adhesive binder is properly set or cured by the time it reachesthe end of the chamber. When the web material is taken down from thedrying rack it is wound up into rolls or cut into sheets suitable forsale. V

Figure 4 is a greatly enlarged perspective view of a piece of fibrousweb 38 made by electrically interweaving and felting several fibrousmembranes as described above. This illustration shows roughly thearrangement of the individual fibres 39 within the web structure. Theyare so interwoven or interlocked as to form the equivalent of a wovenfabric and the heterogeneous arrangement of the individual fibresextends in a multiplicity of non-parallel planes throughout the webstructure. Since there is no discernible line of demarcation between theseveral membranes which make up the web 38 there is no tendency for theweb to delaminate during use.

A modification of the present invention provides for the production offibrous webs of great tensile strength and resistance to crosswisetearing for use under very severe conditions. Mechanical reinforcingmeans, of metallic or nonmetallic nature, can be built into the web inthe course of its construction. For example, spaced strands of cottonthread, string, synthetic resinous filaments or fine diameter wirecan beintroduced onto the carded layers of fabric as the web is being formed.Spools of the stranded materials may be mounted on a suitable framework(not shown) and the reinforcing material fed into the deposited membraneas the web is built up by the apparatus shown in Figure l. The inclusionof the reinforcing strands may be uniform throughout the web structureor it may be limited to the insertion of a single layer of reinforcingfabric or thread positioned at the most advantageous point in the web. Awave form type of reinforcement is produced by oscillating the frameworkwhich carries the spools or reels of stranded material. 1

As is apparent from the above description of the electro-static methodof forming felted fibrous webs, there are numerous advantages over theprior art in addition to those already recited. By the use of patternedor grid-like electrodes it is possible to provide a patterned orvariable weaving unattainable by dependence upon air currents for anyweaving action. Also, the present process permits of close control overeach and all of the electro-static fields separately or cooperatively asdesired; for example, the strength of the fields may be varied dependingupon the thickness of the membranous layers deposited, and closelymaintained so as to avoid damage or disturbance to the. membranes beforedeposition. Also, lateral weaving of the fibres can be easilyaccomplished by positioning electrodes at the sides or by a vibration orsideways movement of the upper and/or lower electrodes of all or anyparticular electrode pair.

While the preferred embodiment of the invention has been specificallyillustrated and described, it is to be understood that the invention maybe otherwise embodied and practiced within the scope of the appendedclaims.

Iclaim: Y

1. The methodof manufacturing flexible fibrous webs of non-lamellarstructure which comprises feeding a plurality of carded fibrousmembranes assasvs from carding cylinders onto a moving endless support,passing said carded fibrous membranes through an electrostatic fieldafter removal from the carding cylinders whereby the individual fibresof each fibrous membrane are electrically charged and brought intointerlocking position with the fibres of adjoining membranes withoutdisruption of the membranous structure, compacting the resulting fibrousweb and removing it from said support.

2. In the process of making flexible fibrous webs having a non-lamellarstructure from a plurality of superimposed carded fibrous membranes ofunwoven nature the step which comprises passing the individual membranesthrough an electrostatic field after removal from the carding cylindersto impart an electrical charge to the individual fibres thereof andcause an intermingling and weaving together of the fibres of onemembrane with the fibres of adjoining membranes without disruption ofthe membranous structure.

3. The method of manufacturing flexible fibrous webs of non-lamellarstructure which comprises feeding a carded fibrous membrane upon amoving endless support, exposing said membrane to the influence of anelectrostatic field to impart an electrical charge to the individualfibres and bring about a raising of the ends thereof, superimposingsimilar fibrous membranes upon the upended fibres of the originallydeposited membrane so that the fibres of the two commingle, repeatingthe aforementioned steps until a web of the desired thickness isobtained, compacting the web and removing it from said support.

4. The method of manufacturing flexible fibrous webs of non-lamellarstructure which comprises feeding a plurality of carded fibrousmembranes from carding cylinders onto a moving endless support, passingsaid carded fibrous membranes through an electrostatic field afterremoval from the carding cylinders whereby the individual fibres of eachfibrous membrane are electrically charged and brought into interlockingposition with the fibres of adjoining membranes without disruption ofthe membranous structure, adding a flexibilized adhesive binder to theweb, compacting the web and removing it from said support.

5. The method of manufacturing flexible fibrous webs of non-lamellarstructure which comprises feeding a plurality of carded fibrousmembranes from carding cylinders onto a moving endless support, passingsaid carded fibrous membranes through an electrostatic field afterremoval from the carding cylinders whereby the individual fibres of eachfibrous membrane are electrically charged and brought into position forinterlocking with the fibres of adjoining membranes without disruptionof the membranous structure, applying an adhesive binder to the web,compacting the web and removing it from said support.

6. In the process of making flexible fibrous webs having a non-lamellarstructure from a plurality of superimposed carded fibrous membranes ofunwoven nature, the steps which comprise passing the individualmembranes through a unidirectional electrostatic field to impart anelectrical charge to the individual fibres thereof and distend thefibrous membranes by upending and agitating the individual fibresthereof and then passing the distended fibrous membranes through analternating current electrostatic field to cause an intermingling andinterweaving of the still electrified fibres of one membrane with thefibres of adjoining membranes.

- ROMIE L. MELTON.

